Systems for determining the properties of an incident electromagnetic signal have a wide variety of applications. For example, mariners and aviators often make use of such systems for purposes of navigation. In addition, these systems may be applied in the military context to surveil troop movements and evaluate enemy communications systems.
Incident signals may be processed to generate a wide variety of information related to the signal. For instance, a signal may be processed to determine the direction of arrival of the signal. The most common direction finding systems include monopulse architectures and phase interferometer systems. These designs make use of a measurement of the time-of-arrival of the source signal upon the antenna array elements. This measurement is generally manifested as a phase measurement due to the accuracy with which time may be inferred when the baseline is a significant fraction of the wavelength. In conventional systems, the antenna elements are configured such that (a) they are of the same design, (b) they have the same orientation, and they (c) have spatial separation (i.e. baseline separation) that is a significant fraction of a wavelength if not multiple wavelengths of the wavelength of interest. As a consequence of these design considerations, signals of interest that have a substantial wavelength call for large spatial separations, increasing the bulk and decreasing transportability of conventional systems.
In addition to issues of size, operation of conventional antenna arrays may be complicated by the tendency of elements to radiate in response to an incident beam. Specifically, incidence of an electromagnetic wave within one element within an antenna array may cause that element to generate an induced electromagnetic wave. This induced electromagnetic wave may impair detection of the electromagnetic wave of interest within other elements and reduce the utility of the system as a whole.